rb_wb_protected_newobj_of(), pass the WB_PROTECTED
information explicitly.
* internal.h: use introduced functions by NEWOBJ_OF().
`flag' is immediate value, so that C compilers can
solve them at compile time.
* include/ruby/ruby.h: add a commnent about that.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52346 b2dd03c8-39d4-4d8f-98ff-823fe69b080e